Certain emergency showers are installed in laboratory and/or industrial applications where personnel may need to wash or flush toxic substances from their bodies in situations where a constant source of water is not readily available. Typically, these showers include a reservoir and either provide water pressure using a pump or through the use of gravity. The reservoir-based emergency showers that use a pump to create a relatively constant pressure and hence flow, require power that is typically obtained from a battery or gasoline-driven generator in remote areas or from typical power outlets in less remote areas.
Known gravity-fed reservoir-based emergency showers rely on head pressure, that is, the pressure created by the weight of the water above the shower head. One problem with known gravity-fed showers is their inability to maintain a substantially constant flow rate during the entire period of use. When a known shower is initially activated for use, the head pressure is relatively high due to the water in the reservoir. The high initial head pressure results in a flow rate of water and pressure through the shower head that is higher than desired. Also, as the shower reservoir drains during use, the head pressure decreases, resulting in a consequent undesirable decrease in the flow rate and pressure of the water through the shower head.
A varying flow rate during use is problematic especially for emergency usage as a sudden high initial flow rate may be unpleasant and even injurious to users, and as the emergency washing function becomes less effective with a decreasing flow rate. In certain cases, the flow rate of known gravity-fed showers may drop below about 20 gallons per minute during a time period of about 15 minutes, which is the minimum required flow rate for emergency showers for compliance with ANSI standards. In addition, due to the decreasing effectiveness of the water flow over time, an overall larger volume of water may be needed to complete the emergency needs of users. To compensate for this problem, certain conventional systems increase the volume of the water reservoir or supplement the reservoir with another source of water. In certain conventional systems, constant flow rate devices, such as constant flow rate valves that deliver a constant flow rate regardless of pressure within a predetermined range, are employed to address the issue of decreasing flow rate over time. However, known constant flow rate valves are not designed to control pressure, are not adjustable, require a minimum pressure differential across the valve, and tend to wear out.